During a Tuesday press conference in Moscow, KGB-officer-turned-parliamentarian Andrei Lugovoi holds papers about the 2006 poisoning of former Russian agent turned Kremlin critic Alexander Litvinenko in London that he said he got from Scotland Yard,

Moscow — The murder of former Russian spy Alexander Litvinenko in London just over six years ago, using what must be the world's most exotic poison, radioactive polonium 210, has never been solved and remains the subject of conflicting narratives and still-deepening intrigue over who may have killed him and why.

Now it appears that a British public inquest that aimed to find definitive answers to those questions, slated to open in May, may have virtually no chance of getting to the bottom of it.

On Tuesday, the main suspect in the case, Russian KGB-officer-turned-parliamentarian Andrei Lugovoi, said he will not travel to Britain to give testimony or even provide evidence via video link.

"I have come to the conclusion that the British authorities will not give me an opportunity to prove my innocence and that I will not be able to find justice in Great Britain," Mr. Lugovoi told a Moscow press conference.

"I have definitely lost my faith in the possibility of an unbiased investigation of this case in Great Britain. I have to state that I am withdrawing from the coroner’s investigation and will no longer participate in it," he said.

No one denies that Lugovoi and his business partner Dmitry Kovtun met with Litvinenko in a London bar on the day he fell ill. British investigators later established that Litvinenko's teacup at that meeting was contaminated with polonium-210, and thus was almost certainly the murder weapon. Traces of polonium, a substance that's almost impossible to obtain except by governments, were later found in Mr. Kovtun's apartment in Germany and on the clothes of both Kovtun and Lugovoi.

Britain demanded at the time that Lugovoi be returned to London to stand trial for murder. But Russia refused, saying the Russian Constitution prohibits the extradition of Russian citizens. Lugovoi was subsequently elected to the State Duma on the ticket of the pro-KremlinUnited Russia party, where he is still a member enjoying parliamentary immunity.

The upcoming inquest, where witnesses must testify under oath, has been regarded as the last chance to unravel all the conflicting stories and perhaps arrive at the truth.

The main suspicion in the West all along has been that Litvinenko was killed on the order of Russian authorities because he had publicly disclosed secrets of the FSB security service and then defected to Britain in 2000, where he continued to make dark and sweeping allegations against Russian President Vladimir Putin and his government.

A good deal of the evidence since dredged up by Western investigative journalists points to Russia -- if not the Kremlin directly -- as the source of the polonium that killed him and probably the motive for doing so as well.

The Russians have countered with various theories, including that Litvinenko may have been murdered by his sponsor and friend, renegade Russian oligarch Boris Berezovsky, in a plot to blame Russia for poisoning an outspoken critic and blacken the reputation of Mr. Putin.

Lugovoi has argued that Litvinenko must have obtained the polonium on his own, and either killed himself with it or was murdered by someone else. Last year Lugovoi took a lie detector test in Moscow, widely covered by Russian media, which reportedly upheld his claim of noninvolvement in Litvinenko's death.

Complicating the picture are persistent allegations that, after receiving asylum in Britain in 2001, Litvinenko went to work for the British intelligence service MI6, providing information about the FSB and the activities of the Russian mafia.

Though Litvinenko's widow earlier denied that her husband had been working for British secret services, her lawyer recently told the Kremlin-funded RT network that "at the time of his death Litvinenko had been for a number of years a regular and paid agent and employee of MI6 with a dedicated handler whose pseudonym was Martin."

The Kremlin's Investigative Committee, Russia's top police body, has conducted its own investigation into the affair -- which has now been suspended -- and its unsurprising tentative conclusion is that Lugovoi was not the killer, but a victim who got contaminated with polonium through his contact with Litvinenko and then was unjustly accused of the crime.

On Tuesday Lugovoi insisted there were plenty of suspects who might have killed Litvinenko. His alleged employment with MI6, his reported assistance to Spanish authorities in tracking down Russian mafia activities, and other dangerous freelance activities added up to a "lifestyle that earned him all sorts of open and covert enemies," he added.

Now that Lugovoi has refused any further participation in the public inquest, we may never find out.